Effective auto-alignment and tracking of transceivers for visible light communication in data centres

In recent years, extensive investigations have been made on high-speed visible light communication (VLC) for indoor applications including data centres. For high-speed VLC systems, precise alignment between the VLC transceivers is usually required to establish an optical link with less optical loss. In this paper, an effective scheme of auto-alignment and tracking of transceivers is proposed for practical VLC systems with a high-speed camera for location of the target light source and a two-axis gimbal for initial auto-alignment between transceivers. To explore the feasibility of the proposed scheme, real-time dynamic 200 Mb/s carrierless amplitude-phase (CAP)-VLC transmission is experimentally demonstrated in >= 3 m VLC links with red light emitting diodes (LEDs) at an angular accuracy of <= 0.02 degrees (0.35 mrad), a tracking speed of <= 27 degrees/s and a latency of <= 21 ms. The proposed scheme can also be applied for coarse alignment in highspeed laser-based free space optical communication (FSO) systems with visible beacons. 10 Gb/s on-off keying (OOK) transmission is successfully demonstrated over a 1.8 m FSO link with the coarse alignment and the spatial light modulator (SLM)-based fine alignment. Experimental results indicate good flexibility and effectiveness of the proposed scheme for an FSO system with high spatial efficiency and low cabling complexity in data centres.